Pan-Continental Droughts in North America over the Last Millennium
Pan-Continental Droughts in North America over the Last Millennium
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DOI：
10.1175/jcli-d-13-00100.1
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发表时间：
2014-01-01
影响因子：
4.9
通讯作者：
Cook, Edward R.
中科院分区：
文献类型：
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作者：
Cook, Benjamin I.;Smerdon, Jason E.;Cook, Edward R.
区域性干旱在北美很常见，但包括2012年事件在内的跨多个区域的泛大陆干旱相对于单一区域事件来说是罕见的。在这里，树木年轮派生的北美干旱地图集被用来调查干旱的变化在四个地区在过去的千年，重点是泛大陆干旱。在中世纪气候异常（MCA）期间，中部平原（CP），西南部（SW）和东南部（SE）地区经历了干燥的条件和干旱的发生率增加，西北部（NW）经历了几次延长的多雨。西南部和CP的MCA干旱增强表现为数十年的特大干旱。值得注意的是，这些地区的特大干旱在时间和持续时间上各不相同，这表明它们是受当地动态影响的区域性事件，而不是统一的大陆规模现象。没有泛大陆干旱发生的趋势，即三个或更多地区同时发生干旱。西南、CP和SE（西南+CP+SE）干旱是最常见的，发生在所有年份的12%，在12和13世纪达到顶峰;涉及其他三个地区的模式发生在大约8%的年份。南方涛动指数（拉尼娜条件）的正值与西南、CP和SE（SW+CP+SE）干旱和西南、CP和NW（SW+CP+NW）干旱有关，而CP、NW和SE（CP+NW+SE）干旱与太平洋年代际振荡和大西洋多年代际振荡的正值有关。泛大陆干旱虽然相对罕见，但在古记录中存在，并与确定的气候变率模式有关，这意味着季节性可预测性的潜力。假设稳定的干旱遥相关，这些事件将仍然是未来北美水文气候的一个重要特征，其严重程度可能会随着其他预期的水文气候响应增加温室气体强迫而增加。
Regional droughts are common in North America, but pan-continental droughts extending across multiple regions, including the 2012 event, are rare relative to single-region events. Here, the tree-ring-derived North American Drought Atlas is used to investigate drought variability in four regions over the last millennium, focusing on pan-continental droughts. During the Medieval Climate Anomaly (MCA), the central plains (CP), Southwest (SW), and Southeast (SE) regions experienced drier conditions and increased occurrence of droughts and the Northwest (NW) experienced several extended pluvials. Enhanced MCA aridity in the SW and CP manifested as multidecadal megadroughts. Notably, megadroughts in these regions differed in their timing and persistence, suggesting that they represent regional events influenced by local dynamics rather than a unified, continental-scale phenomena. There is no trend in pan-continental drought occurrence, defined as synchronous droughts in three or more regions. SW, CP, and SE (SW+CP+SE) droughts are the most common, occurring in 12% of all years and peaking in prevalence during the twelfth and thirteenth centuries; patterns involving three other regions occur in about 8% of years. Positive values of the Southern Oscillation index (La Nina conditions) are linked to SW, CP, and SE (SW+CP+SE) droughts and SW, CP, and NW (SW+CP+NW) droughts, whereas CP, NW, and SE (CP+NW+SE) droughts are associated with positive values of the Pacific decadal oscillation and Atlantic multidecadal oscillation. While relatively rare, pan-continental droughts are present in the paleo record and are linked to defined modes of climate variability, implying the potential for seasonal predictability. Assuming stable drought teleconnections, these events will remain an important feature of future North American hydroclimate, possibly increasing in their severity in step with other expected hydroclimate responses to increased greenhouse gas forcing.